Recently, as oil prices have increased, researches on hybrid-type construction machines having improved fuel efficiency by storing surplus power of an engine in a battery and supplying power to the engine having insufficient power from the battery have been actively conducted.
As such, a system using an engine and an electric motor as a common power resource and including an electric energy storage device is referred to as a hybrid system. For example, the hybrid system includes a hybrid car and a hybrid system for heavy equipment, such as an excavator.
In the meantime, a general excavator system performs an operation of swing or traveling a boom, an arm and a bucket which are final loads by the medium of oil pressure taking an engine as a power resource. Contrary to this, in a hybrid excavator system, two motors and an electricity storage device are additionally installed in a general excavator, so that the overall efficiency of the excavator system may be improved. A main component added to the hybrid excavator system includes a motor, an electricity storage device, an inverter and a converter.
FIG. 1 is a configuration diagram illustrating a general hydraulic excavating apparatus.
As illustrated in FIG. 1, the general hydraulic excavating apparatus includes an engine 110, a hydraulic pump 120, a control valve 130, a boom/arm/bucket cylinder 140, a swing motor 150 and a travelling motor 160.
The hydraulic pump 120 is directly associated with the engine 110, to supply pressurized oil to the control valve 130. That is, the hydraulic pump 120 rotates the hydraulic pump with rotation force of the engine 110 and supplies the pressurized oil to the oil pressure main control valve 130.
The control valve 130 may control the pressurized oil to be provided to an actuator (for example, the boom/arm/bucket cylinder 140, the swing motor 150 and the travelling motor 160) by controlling the pressurized oil supplied from the hydraulic pump 120. That is, the control valve 130 drives the excavating apparatus by supplying the pressurized oil to the boom/arm/bucket cylinder 140, the swing motor 150 and the travelling motor 160 according to a lever instruction of a driver.
The boom/arm/bucket cylinder 140 receives the pressurized oil provided from the control valve 130, to drive the boom, the arm and the bucket of the excavating apparatus.
The swing motor 150, which is a hydraulic motor for swing, receives the pressurized oil provided from the control valve 130, to rotate an upper swing body of the excavating apparatus. Further, when the control valve 130 interrupts the supply of the pressurized oil, the swing motor 150 acquires braking force in a stop state.
The travelling motor 160 receives the pressurized oil provided from the control valve 130, to drive a travelling device of the excavating apparatus.
FIG. 2 is a configuration diagram illustrating a general hybrid excavator.
As illustrated in FIG. 2, the general hybrid excavator includes an engine 110, a hydraulic pump 120, a control valve 130, an engine auxiliary motor 210, an engine auxiliary inverter 220, an inverter 230 for swing, a swing motor 240 including a brake, an energy storage unit 250, a hybrid controller 260 and a direct current (DC)/DC converter 270. Here, the hybrid controller 260 is connected with a current detector 261 for detecting a current between the energy storage unit 250 and the DC/DC converter 270. Further, the hybrid controller 260 is connected with a voltage detector 262 for detecting a voltage between the energy storage unit 250 and the DC/DC converter 270.
The general hybrid excavator may obtain driving force by the oil pressure through the engine 110, the engine auxiliary motor 210 directly connected with the engine 110, the hydraulic pump 120 directly connected with the engine auxiliary motor 210, the control valve 130 for controlling the pressurized oil of the hydraulic pump 120 and an actuator for driving the boom, the arm and the bucket.
The engine auxiliary motor 210 directly connected with the engine 110 is operated as a motor when output of the engine 110 is insufficient. However, when the output of the engine 110 is sufficient, the engine auxiliary motor 210 directly connected with the engine 11 is operated as a generator.
The engine auxiliary inverter 220 operates the engine auxiliary motor 210 as the motor or the generator. The engine auxiliary inverter 220 drives the motor under control of the hybrid controller 260.
An input terminal of the engine auxiliary inverter 220 includes a DC link capacitor 221 that is a predetermined capacitor. The DC link capacitor 221 stabilizes an input voltage of the engine auxiliary inverter 220, and when the engine auxiliary motor 210 is operated as the generator, the DC link capacitor 221 performs a function of temporarily storing generated energy.
The swing motor 240 drives the upper swing body of the hybrid excavator. Here, the inverter 230 for swing which drives the swing motor 240 is connected to the DC link capacitor 221 that is a DC voltage terminal.
The inverter 230 for swing, which drives the swing motor 240, performs an acceleration driving and a deceleration driving according to lever control by a user operating the hybrid excavator. The inverter 230 for swing makes the swing motor 240 be operated as a motor at the time of the acceleration. However, the inverter 230 for swing makes the swing motor 240 to be operated as a motor at the time of the deceleration. That is, the inverter 230 for swing converts rotational inertia energy of the upper swing body of the hybrid excavator to electric energy, to supply the converted electric energy into the DC link capacitor 221 of the DC voltage terminal.
The energy storage unit 250 performs a function of storing electric energy and is connected to the DC/DC converter 270 which controls charging and discharging. The DC/DC converter 270 makes a control such that the voltage of the DC link capacitor 221 that is the DC voltage terminal is constant.
The hybrid controller 260 controls the engine auxiliary inverter 220, the inverter 230 for swing and the DC/DC converter 270. The hybrid controller 260 determines an output quantity when the engine auxiliary motor 210 is operated as the motor and an output quantity when the engine auxiliary motor 210 is operated as the generator by controlling a flow of the entire power of the hybrid excavator. Further, the hybrid controller 260 makes a control such that a quantity of electric energy stored in the energy storage unit 250 is maintained at a voltage within a predetermined range.
FIG. 3 is a configuration diagram illustrating a hybrid excavator different from that illustrated in FIG. 2.
The different hybrid excavator illustrated in FIG. 3 generally has the same construction as that of the general hybrid excavator illustrated in FIG. 2, but the different hybrid excavator illustrated in FIG. 3 does not include the DC/DC converter between the engine auxiliary inverter 220 and the energy storage unit 250.
Hereinafter, a construction difference will be described by comparing the construction of the general hybrid excavator illustrated in FIG. 2 and the construction of the different hybrid excavator illustrated in FIG. 3.
The input terminal of the engine auxiliary inverter 220 is formed with the DC link capacitor 221 that is a predetermined capacitor and the large capacity energy storage unit 250 in parallel. Here, ripple current by charging and discharging according to the operation of the engine auxiliary inverter 220 is configured to be supplied from or charged in the DC link capacitor 221.
The different hybrid excavator includes the energy storage unit 250 for storing energy. The energy storage unit 250 is configured to charge surplus energy of the engine 110 and discharge energy in the operation of the upper swing body. The hybrid controller 260 determines the output quantity when the engine auxiliary motor 210 is operated as the motor and the output quantity when the engine auxiliary motor 210 is operated as the generator by controlling the flow of the entire power of the hybrid excavator. Further, the hybrid controller 260 makes a control such that a quantity of electric energy stored in the energy storage unit 250 is maintained at a voltage within a predetermined range.
In the meantime, the inverter 230 for swing, which drives the swing motor 240, includes six semiconductor switches, an inverter controller for controlling on/off of the semiconductor switch and a DC-terminal capacitor for stabilizing voltage of the input terminal in order to drive a three-phase motor.
In order to supply current to the swing motor 240, the inverter controller controls voltage applied to the swing motor 240 by adjusting an on/off pulse width of the six switches.
The semiconductor switch device is damaged when over-current is generated or by over-voltage. In order to prevent the damage, the inverter controller of the inverter 230 for swing switches off the six switches in order to protect the inverter 230 for swing upon the occurrence of the over-current and the over-voltage.
When failure such as the over-current and the over-voltage of the inverter 230 for swing is detected during the rotation of the upper swing body, so that the inverter controller switches off the switches, the upper swing body freely rotates until a braking operation by rotational inertia. In this case, there is a problem in that the risk of accidents due to a collision between a neighboring object and the upper swing body is greatly increased.
That is, when an abnormal state, such as the over-current and the over-voltage, of the motor or the inverter driving the motor is generated in the hybrid excavator employing the electric swing motor 240 so as to drive the upper swing body, the inverter for swing in the related art interrupts the power supply of the motor. Then, the upper swing body freely rotates until the braking operation, which has a problem in that the risk of accidents is substantially increased.
In order to solve the problem, a method of controlling an inverter for effectively stopping a motor when failure of an inverter driving a motor is detected has been urgently required.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.